Sexuality is driven by nature. Also, sexuality does not define an individual, thus love your daughter for who she is. All children explore sexuality as a normal part of development. And although sexual orientation can't be chosen, people have a choice of how they express their sexuality.
If being bisexual does not pose a problem for your daughter, it should not be a problem for anybody else. If your daughter is confused about her sexuality, let her figure it out on her own without judging her choices in this matter. You may serve as a supportive resource by providing her with reliable information when she asks for it.